Rules for the dates of events that are recurrent (ie. come back, usually, every year). Examples are: Christmas (every year on December 25) aor Good Friday (2 days before Easter). Recurring holidays are often referred to, simply, as holidays.

One-Time Dates

Dates of events that will occur once only. Examples are "300 days before the year 2000" or "Opening of the XXVth Olympics in Atlanta".